The purpose of this work is to characterize several toxic factors of Group A streptococci that may play a role in streptococcal pathogenesis. The study of streptolysin S (SLS) includes its purification, characterization, and determination of it mechanism of secretion from the bacterium. Since lipoteichoic acid (LTA) was discovered to be a carrier molecule for the SLS hemolysin, the relationship of the two in the bacterium and in possible pathogenic roles are being explored. The differences in binding to several different carriers such as detergents, synthetic polynucleotides, and LTA is being utilized both for purification of the toxin and to distinguish the different intracellular forms of the toxin. Group A streptococcal cell walls which can produce severe rheumatoid-like arthritis in rats are being utilized to determine the genetic differences in host response which lead to the arthritis. Macrophages and lymphocytes of responder and non-responder rats are being analyzed and compared to determine the basis of response.